Abstract: Methane and acetylene are the most important characteristic gases when the transformer breaks down. In order to meet the demand for detecting the concentration of the trace CH₄ and C₂H₂ dissolved in the transformer, the laser photoacoustic spectroscopy gas detection technology was adopted. By analyzing the near-infrared absorption spectrum of CH₄ and C₂H₂ gas, the appropriate laser light source was selected and the laser modulation parameters were determined. A set of photoacoustic spectroscopy trace CH₄ and C₂H₂ gas detection system with dual laser light source and a non-resonant photoacoustic cell were designed, and the detection sensitivity and low concentration detection error of the system for CH₄ and C₂H₂ gas was obtained. The result shows that CH₄ and C₂H₂ have good response linearity in the volume fraction range of 0~1000×10^-6 and 0~500×10^-6, respectively, and the responsivities are 5.8969μV and 16.1831μV per 10^-6 volume fraction, respectively. The system is tested for repeatability and accuracy using low-content CH₄/C₂H₂ mixed gas. The maximum absolute error of detection is 0.30×10^-6 when the CH₄ volume fraction is 3.00×10^-6, and the maximum absolute error of detection is 0.20×10^-6 when the C₂H₂ volume fraction of 0.50×10^-6. The research results meet the technical index requirements of measurement error and achieve high-sensitivity detection of trace CH₄ and C₂H₂.